This invention relates to movable load carrying mechanisms such as shuttle tables and more particularly to a drive arrangement for such a load carrying mechanism.
Shuttle tables known in the art, which tables are frequently used in automated storage and retrieval systems, often utilize chains coupled between a stationary frame and a movable table surface to transmit power between a source and the movable table surface. Although conventional chain linkages are generally satisfactory when the tables are used to carry relatively light loads, these chain structures have proved to be generally unsatisfactory when called upon to handle heavy loads. This is due primarily to the fact that these chains must be offset or canted as they are wrapped about the sprockets or sheave nests located adjacent the forward and rearward ends of the table and this offset places substantial stress on the chains causing relatively high rates of wear. Additionally, as the loads carried by the shuttle table are increased, the thickness or weight of the chains utilized to drive the table must, of course, be increased. This in turn necessitates the use of greater offsets and these greater offsets result in even higher rates of wear. Further, because the locations at which the chains are connected at each longitudinal end of the table are not symmetrical relative to the longitudinal center-line of the table, skewing forces are applied to the table when it is driven. It will be readily understood of course that rapid chain wear is undesirable for reasons beyong the mere cost of the chain which must be replaced. Since the table is inoperable during the period of chain replacement, the warehouse section served by the particular table is also out of service during this period and it is this effect of rapid chain wear which results in the greatest cost and is the most unacceptable. Additionally, the aforementioned skewing forces cause problems in accurately positioning the table and cause misalignment of the table, so that, even if the table is operable, its utility is decreased and may even be of virtually no value.